Abstract
How to prevent the cracking of tunnel lining concrete under a high-temperature and low-humidity environment has gradually become a challenge faced by the engineering community. Actually, the concrete structure will be restrained, which easily leads to cracking. Aiming at this problem, a self-restraint device of concrete specimens was designed in this paper, which aims to more realistically simulate the restrained state of concrete structures during construction. SEM, EDS and XRD detection methods were used to study the macroscopic and microscopic properties of an early-age restrained concrete specimen under a high-temperature and low-humidity environment, and the results were compared with those of a non-restrained concrete specimen. The results show that the change in the internal relative humidity of the concrete was an extremely slow process, and the response rate of the internal humidity of the concrete was much slower than that of the temperature. A cubic curve model was used to fit the measured concrete damage degree with the loading age, and the fitting effect was good. Under the environment of high temperature and low humidity, the loading age from the 0.6th day to the 1st day was the period of a relatively large fluctuation in the concrete temperature and humidity, and the restraint would aggravate the damage of the concrete. The damage degree increased with the increase in the loading age, the microcracks gradually increased and, finally, macrocracks were formed. The restraint effect was to intensify the formation of microcracks, affect the hydration of the cement at the micro level and, finally, increase the risk of concrete cracking perpendicular to the restrained direction at the macro level. The research results may provide guidance for research on the cracking mechanism of tunnel lining concrete constructed under a high-temperature and low-humidity environment.
Highlights
A large number of engineering practices have proved that 80% of concrete structural cracks are mainly caused by the non-load stress generated by the concrete material itself or under the action of environmental temperature and humidity changes [1]
The temperature measured by sensor T-1-3 fluctuated to a certain extent around the 0.6th day of the loading age, but the temperature eventually rose rapidly to 50 ◦ C and remained stable
Through the combination of macro experiments and micro-SEM, EDS and XRD detection methods, the following main conclusions were obtained for the early-age restrained concrete specimen under the environmental conditions of 50 ◦ C and 30% relative humidity
Summary
A large number of engineering practices have proved that 80% of concrete structural cracks are mainly caused by the non-load stress generated by the concrete material itself or under the action of environmental temperature and humidity changes [1]. How to prevent cracks in tunnel lining concrete constructed in a high-temperature and low-humidity environment [15] has gradually become a problem faced by the engineering community, which has attracted close attention. The concrete structure will be restrained, either restrained by the external rock base [21], restrained by the deformation difference caused by the temperature gradient inside [22] or restrained by the drying shrinkage of the structural surface by the internal concrete [23]. The research results may provide guidance for the study of the cracking mechanism of tunnel lining concrete under a high-temperature and low-humidity environment
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